Computing resources may be provided by a variety of different host computers operating with different operating systems such as Microsoft Windows®, Linux, SunOS®, HP-UX®, and AIX®. Alternatively, computing resources may be provided by several powerful host computers each providing several virtual machines (VM). A VM may provide an execution environment for applications that isolates the applications from the underlying machine. The VM may provide an emulation of an operating system, such as Microsoft Windows®, Linux, SunOS®, HP-UX®, AIX® and others, that the applications may execute on.
Digital storage or memory may be organized into addressable segments referenced by a logical unit number (LUN). In some cases, the portion of memory may be referred to as a LUN. Some virtual machines may be able to address a limited number of LUNs.
Host computers may use multiple central processing units (CPUs) to distribute the work load of the host computer. Increasing the number of CPUs in a host computer generally increases the processing power of the host computer, but efficiency may drop off with increased numbers of CPUs. For example, while an eight CPU host computer may operate at high CPU utilization rates, a sixteen CPU host computer may operate at diminished CPU utilization rates because of competition among CPUs to access a shared memory bus. In general, the architecture of internal memory busses and external connectivity and the character of the applications and/or virtual machines that run on a multi-CPU host computer effect the efficiency of use of the multiple CPUs.